1. Field of Invention
The present invention relates to a system for preventing knocking and a method for controlling the same. More particularly, the present invention relates to a system for preventing knocking and a method for controlling the same that prevent knocking by injecting a sub fuel including ethanol having high octane number to a combustion chamber in a case that the knocking occurs.
2. Description of Related Art
Generally, efficiency of spark ignition gasoline engines can be improved by operating the engines in a high compression ratio or reducing a size of the engine. If the engine is operated in the compression ratio or the size of the engine is reduced, however, knocking may occur and occurrence of the knocking may deteriorate performance of the engine.
In an end of combustion stroke, pressure and temperature at an end-gas zone in of a combustion chamber may increase and fuel may be self-ignited. The knocking may occur due to the self-ignition of the fuel. If the knocking occurs, the fuel is burned quickly and a piston may be damaged by vibrations. In addition, since combustion pressure is quickly lowered after reaching maximum pressure, performance of the engine may be deteriorated.
The engine compression ratio was lowered or ignition timing was lagged in order to prevent occurrence of the knocking according to prior arts. In this case, the performance of the engine may be deteriorated and fuel economy may be decreased.
In addition, it has been developed that ethanol having higher octane number than gasoline is directly injected to the combustion chamber and the ethanol is adapted to move to the end-gas zone by using a strong swirl flow. However, a method of injecting ethanol by using swirl flow cannot be applied to a gasoline direct injection engine in which the swirl flow is weak. In addition, if the ethanol is moved to the end-gas zone by using the swirl flow, precise operation may not be guaranteed.
The information disclosed in this Background section is only for enhancement of understanding of the general background of the invention and should not be taken as an acknowledgement or any form of suggestion that this information forms the prior art already known to a person skilled in the art.